Using Sweat to Charge Your Cell Phone

Imagine using daily exercise not just to power your body, but also your cell phone. That’s what a team of scientists at the University of California-San Diego (UCSD) are working on, with the aid of a temporary tattoo that monitors a person’s progress during exercise and generates power from their sweat.

Tiring exercise triggers a process called “glycolysis,” which produces energy to maintain the exercise, as well as lactate, which can be detected in your blood. Professional athletes evaluate their fitness and the quality of their training programs by monitoring their lactate levels. Doctors do it for patients with heart or lung disease, both of which cause abnormally high levels of lactate. Current monitoring for athletes is clumsy, though, because blood samples need to be collected and analyzed during exercise — not after.

The UCSD team came up with a faster, easier, and less intrusive way to get this done. They printed a flexible lactate sensor onto paper used to transfer temporary tattoos to skin. The sensor includes an enzyme that removes electrons from lactate, which generates a weak electrical current. The researchers then applied the tattoos to the upper arms of 10 healthy volunteers and measured the electrical current produced during increasingly strenuous exercise on a stationary bicycle over a half-hour. Grasping the significance of their discovery, they built a sweat-powered “biobattery.”